Facile fabrication of ZnO decorated ZnFe-layered double hydroxides @ biochar nanocomposites for synergistic photodegradation of tetracycline under visible light

To explore effective treatment of antibiotics-contaminated water using visible light-responsive photocatalyst, a series of ZnO decorated ZnFe-layered double hydroxide @ biochar (ZnO/ZnFe-LDH@BC) nanocomposites were obtained via a facile hydrothermal method. The fabricated nanocomposites exhibited uniform distribution of ZnO/ZnFe-LDH on BC matrix, allowing more active sites of ZnO/ZnFe-LDH to be utilized. The BC matrix brought widened visible-light absorbance, narrowed bandgap, and improved charge separation and transfer. During photocatalytic degradation of tetracycline (TC) under visible LED light, the nanocomposites showed significant enhancement of degradation efficiency, compared to ZnO/ZnFe-LDH or BC alone, indicating a strong synergy between ZnO/ZnFe-LDH and BC. The nanocomposite containing 23.0 wt% of BC (ZnO/ZnFe-LDH@BC0.2) showed optimal performance (achieving 87.7% of degradation within 4 h) in comparison to the reported LDHs@carbon photocatalysts. Alkaline condition and co-existing CO32- ions could enhance the stability and recyclability of the nanocomposites. Additionally, the possible degradation pathway of TC was analyzed via LC-MS and the reduction in toxicity resulting from photocatalytic degradation was confirmed by the culture of mung bean sprouts. This study provides a rational design strategy and performance assessment of LDH-based nanocomposites for the treatment of antibiotics-contaminated water.